Devices for mixing of bone cement must meet a plurality of high requirements. Mixing and application of bone cement are critical moments in many common operations such as joint surgery, neurosurgery and dental surgery, and it is therefore of utmost importance that the mixing equipment is designed as user friendly and safe as possible. The technique for carrying through mixing and the way the cement is applied in the body, drastically affects the quality of the hardened or set bone cement and thus, the term of life of e.g., the hip or knee implant. In the leading mixing systems of today, mixing is therefore conducted under a vacuum, which reduces the porosity and thus, increases the fatigue strength of the hardened or set cement, and the mixed cement is discharged by means of a discharge gun directly from the mixing container, through a tip mounted thereon, to the desired location in the body, e.g., the thigh bone for fixing the hip implant.
Most mixing devices used today require that the person mixing the bone cement, the surgeon or the sterile nurse, themselves open the packages for the cement components, usually a bag for the powder component and a glass ampoule or vial for the liquid component, and pour these into the mixing container. This moment has several risks.
First, there is a risk that the nurse when breaking the ampoule or vial spills liquid and/or cuts herself on the sharp edges formed on the surfaces of fracture of the glass ampoule or vial. Another problem is that the operating personell is subjected to irritating and eventually harmful vapours which are set free from the liquid component in connection with the opening of the ampoule or vial and the transfer to the mixing container. In order to eliminate these problems, several mixing devices have been proposed, see e.g. U.S. Pat. Nos. 5,549,380, 5,551,778, 5,779,356, U.S. Pat. No. Re 35 276 and U.S. Pat. No. 5,588,745, wherein the cement components are transferred to the mixing container without exposing any component to the surrounding air, i.e. in a completely sealed system. Before mixing in said devices, the powder component is kept in the mixing space, while the liquid component is kept either beside or in direct connection with the mixing container in a package adapted particularly therefor. The demand for a specialized package for the liquid component however, causes substantial practical problems. The liquid component requires special pouring into the package particularly adapted therefor, which is a substantial problem of the manufacturing technique since aseptic filling must be practised. Furthermore, the mixing system is limited to mixing of those types of cement which are available in the special packages belonging to the mixing system.
The present invention avoids the above problems since the mixing device makes possible a completely sealed mixing of bone cement with bone cement components packed up in standard packings, i.e. liquid component in a glass ampoule or vial and powder component in a bag. Before mixing, the glass ampoule or vial is placed in a separate outer container which is connected to the mixing container, which contains the powder component. After the sealed system, consisting of container for liquid component and mixing container, has been evacuated by means of a vacuum source, the tip of the glass ampoule or vial is broken off, whereby the liquid component flows into the mixing container and comes in contact with the powder component, thereby initiating the mixing procedure. Since the container is easily modified for differently sized glass ampoules or vials, the device may be used for mixing of all common cement types on the market.
The publication U.S. Pat. No. 5,435,645 relates to a mixing device at which a sealed container--a container with a monomer component--is located in an outer container. The mixing member of the mixing device has a space to which the outer container is adapted and into which said outer container is screwed. Such a construction of the mixing device necessitates manufacture of a special type of monomer container since this container must fit into the outer container which in turn must fit into the mixing member. Furthermore, this mixing device has no mixing means which is provided in the mixing space of the mixing member for advantageous mixing.
The publications WO 97/18031 and SE 500 430 relate to mixing devices at which the outer containers with the sealed containers may be connected to a tubular mixing means and when the sealed containers are opened, the component therein is fed through the tubular mixing means to the mixing space and the component provided therein. Such an embodiment requires a special type of tubular mixing means which must be sealed by means of sealing rods such that air can not flow into the mixing device during mixing. At an embodiment according to the publication WO 97/18031 the outer container is through a hose connected to the side of the mixing member and thus, requires making a hole in the side of the mixing member through which air can flow into the mixing space and/or components flow out of said mixing space when the hose is released.
Since the mixing device according to the invention has the abovementioned characterizing features, harmful exposure to the vapours of the liquid component and other risks are eliminated, it becomes possible to use an outer container for different existing monomer containers at one and same mixing member, mixing may occur under a vacuum and by means of a mixing means provided in the mixing space of the mixing member and there is no risk for penetration of air into the mixing device after bringing together the two components and until mixing is complete.